As produced, e.g., by a fluid bed reactor, such as the reactor shown in U.S. Pat. No. 8,075,692, granular polysilicon typically contains from 0.25% to 3% powder or dust by weight. The powder may render the product unsuitable for certain applications. For example, a product containing such levels of powder is unsuitable for monocrystalline applications since the powder can cause a loss of structure, making single crystal growth impossible.
Wet processes for removing dust (e.g., rinsing, ultrasonic cleaning, etching) have disadvantages because there is complex, costly equipment to maintain, water and/or chemicals are required, and the processing may cause detrimental oxidation of the polysilicon. Thus, there is a demand for a dry process that produces granular polysilicon with reduced powder levels.